1. Field the Invention
This invention is related to a method and medium for selective growth of propionibacteria from mixed culture samples.
2. Brief Description of the Background Art
The use of silage additives has become a widely accepted practice throughout much of the agricultural world. In order to understand how silage additives react with silage, it may be helpful to first review the basic biochemical and microbiological changes that occur during the ensiling process. Immediately upon chopping of, for example, corn, aerobic respiration starts. During this early phase, soluble carbohydrates in the plant tissue are oxidized and converted to carbon dioxide and water. This process will continue until either the oxygen level is depleted or the water-soluble carbohydrates are exhausted. Under ideal conditions, with adequate packing and sealing of the ensiled material, respiration lasts only a few hours. The growth of microorganisms during this period is limited to those that are tolerant to oxygen which includes aerobic bacteria, yeast and molds. These organisms are generally recognized as being negative to the system as they metabolize sugar to carbon dioxide, heat, and water.
Recently it has become known that bacterial inoculants help preserve silage, including both grass silage and corn silage. For example, inoculation with lactic acid bacteria during the fermentation phase can be beneficial to the fermentation process, see for example U.S. Pat. No. 4,842,871 of Hill issued June 27, 1989, as well as the literature references cited therein. For high-moisture corn stability, this increase is probably due to the inoculant enhancing the rate of anaerobic fermentation and pH decrease. This is beneficial because oxidative losses caused by aerobic pH-sensitive microflora in the initial stages are thus avoided. In other silages such as whole corn plant, alfalfa, etc. the inoculant can also have beneficial effects on the digestibility of the silages by causing an increase in the availability of the fiber.
A co-pending and commonly assigned application relates to a bacterial inoculant for silage preservation which aids in stability in the second part of the process that occurs when a silo is opened to the air. This co-pending application, Ser. No. 431,883, Tomes, filed Nov. 6, 1989, the disclosure of which is incorporated herein by reference, in its broad aspects relates to treating silage with a preserving effective amount of the microorganism Propionibacterium jensenii, or the genetic equivalent. As a result, the metabolic products of the propionibacteria aid in assuring a stable product during their aerobic phase, when the silo is open.
It can therefore be seen that there is a continuing need for selective growth of species of Propionibacterium and particularly Propionibacterium jensenii to the exclusion of other species in mixed culture samples, so that Propionibacterium can be isolated for uses peculiar to Propionibacterium, such as use in the invention of the incorporated by reference application.
The primary objective of the present invention therefore is to fulfill the need for a medium which allows selective growth of Propionibacterium from mixed culture samples to the exclusion of other bacteria, particularly Lactobacillus.
Another objective of the present invention is to provide a medium and a method of use of the medium which allows not only growth of Propionibacterium to the selective exclusion of others like Lactobacillus, but also a medium which under proper conditions and selectivity of added agents allows strain selection within the genera of Propionibacterium to allow certain strains of Propionibacterium to grow to the exclusion of others.
A yet further objective of the present invention is to provide a medium composition useful in the methods described herein.
The method and manner of accomplishing each of the objectives of the invention as well as perhaps others will become apparent from the detailed description of the invention which follows hereinafter.